A power cable is an assembly of two or more electrical conductors, usually held together with a sheath. The assembly may be used for transmission of electrical power. Power cables may be installed, for example, as permanent wiring within buildings, buried in the ground, run overhead or exposed. Flexible power cables may be used for portable devices, mobile tools and machinery.
Cables may include three major components: conductors, insulation and protective jacketing. The makeup of individual cables may vary according to application. The construction and material may be determined by the working voltage, current-carrying capacity and environmental conditions.
Power cables may use stranded copper or aluminum conductors. Some cables may include un-insulated conductors for circuit neutral or ground (earth) connection.
The overall assembly may be round or flat. Non-conducting filler strands may be added to the assembly to maintain its shape. Special purpose power cables for overhead or vertical use may have additional elements such as steel or Kevlar structural supports.
Common types of general-purpose cables are regulated by national and/or international codes. These codes define the various wire alloys that may make up a cable, its insulation type, and characteristics including its resistance to chemicals and sunlight.
Commonly-used power cables may contain an un-insulated bare wire for connection to earth ground. Three prong power outlets and plug-cords require a grounding wire. Extension cables often have an insulated grounding wire.
ROMEX is a cable made of solid copper wires with a nonmetallic plastic jacket containing a waxed paper wrapped inner group of at least a pair of 600 volt THWN plastic insulated service wires and a bare ground wire. A common ROMEX cable may thus have three wires: a neutral wire (colored white), a wire providing power to the load (colored black) and a bare grounding wire.
Another common ROMEX variant has a neutral, identified by white coloring, two phase wires: a first conductor (black) and a second conductor (usually red), and an un-insulated copper grounding wire. This type may be generally used for multiple switching locations of a common or shared lighting arrangement, such as for switches located at either end of a hallway, or on both upper and lower floors for stairway lighting.